Some problems of high-voltage transmissions

For a considerable time the voltage of long distance transmissions was limited by the line insulator. Until a few years ago, the transmission line insulator was the same pin type as used in telegraph and telephone lines, differing only by its larger size, by the replacement of glass by porcelain, and by the addition of a few more petticoats, but no radical change had occurred, until the limit of this type was reached at 30,000 to 40,000 volts — with a few 60,000 volt lines of questionable reliability.